The invention relates to measuring mechanical runout of a rotating work piece.
A uniform radius is desirable around the circumference of rotating work pieces such as the rotor work piece of a turbine. Knowing the shape of a work piece relative to ideal roundness may be used to compensate for or reduce vibration induced by rotation of the work piece. Measuring a radius at each circumference along the length of an entire work piece often requires a great deal of time and cost, primarily associated with labor.
“Runout”, generally, is the amount of deviation from a desired rotation radius of a rotor during operation, and can be described in terms of mechanical runout and electrical runout. The mechanical runout of a rotor is the deviation from an ideal circular geometry of the rotor plane during rotation. Accurate measurement of the mechanical runout is necessary to be able to minimize the negative impact of these imperfections on performance, such as vibration of the rotor at operational speeds.
In addition to knowing generally the shape of the surface of a mechanical rotor and how far the rotor is from an ideal circular geometry, there is value in knowing the angular position of each piece of surface information relative to some reference point. Therefore, it is desirable to measure mechanical runout as a function of work piece angular position. Currently available options to accurately measure runout as a function of angular position require (1) a human to manually determine and measure an angular position; or (2) the use of phase reference probes.
Measurements taken at speeds of 15% or lower of rated speeds for the work piece in question are called “slow roll mechanical runout.” The slow roll mechanical runout provides an indication as to whether the work piece will function properly during normal operation, as it is an indication of the irregularities in surface shape.
Currently, the runout is measured in one of a few ways: (1) a complete manual 12-point runout, (2) a semi-manual 12-point runout, (3) use of a high sample rate digital sensor, i.e., a CL profiler, or (4) use of phase reference indicators, which require additional instrumentation.
Other available runout measurement methods require additional instrumentation. Key phasors, encoders, magnets and magnetic field sensors are potential options. Some options, like phase reference probes, may require the work piece to be altered to create an intentionally-machined discontinuity, such as a slot or key way, to serve as a once-per-revolution indicator. Under this method, phase references probes are positioned over a machined discontinuity in the work piece and provide a once-per-turn reference pulse from which the phase angle of the vibration can be determined.